Abstract: The energy balance equation of an isolated structure is established at the moment of maximum earthquake responses. Expressions of elastic vibration energy and plastic energy for isolated layers and non-isolated layers are presented. Then, based on the energy principle, formulas for predicting earthquake responses are derived. Three numerical models, including a top-isolated structure, a storey-isolated structure and a base-isolated structure, are used to validate the accuracy of the predicted responses. Finally, the aseismic properties of the three isolated structures are discussed. Results show that response prediction curves can match well and envelope most of the time history responses for a class of earthquake records. Energy method can be used to predict earthquake responses of isolated structures.